Go with Dulux Spun Mohair. It lands at ΔE 1.2 from Benjamin Moore Gray Owl, which is well inside the "very close" bracket and close enough that you'd struggle to tell them apart on a wall side by side. With an LRV of 66.2 it's a light, airy grey with that same green-blue lean that makes Gray Owl such a chameleon — it'll read soft grey in bright rooms and pick up cooler, almost watery tones in north light.
If you want a slightly lighter, brighter take, Dulux Spiders Web is the backup at ΔE 2.2 and LRV 71.3. It's still a genuinely good match but it's a touch paler and a hair cleaner, so it bounces a bit more light. In a darker room that can be a help; in a bright south-facing space it can tip towards looking a little washed out.
Now the honest bit: why bother matching at all? People usually want a Dulux equivalent because they can't easily get Benjamin Moore mixed locally, or they're working to a trade account that carries Dulux. Both are fair reasons. But if the original spec was Gray Owl and you can get it, Benjamin Moore is worth the small premium — their greys are beautifully balanced and Gray Owl in particular is one of the best in the range.
Whichever way you go, buy a sample pot and test it before you commit. A ΔE of 1.2 is close, but Gray Owl is one of those colours that shifts dramatically with aspect — it can look almost grey-green one minute and cool blue-grey the next. Paint a big swatch (A2 minimum, or a bit of lining paper you can move around), look at it morning and evening, and check it against any fixed elements like flooring or worktops before you order the lot. Match on paper, confirm on the wall.